Coronary artery disease (CAD) is a chronic condition requiring continuous management by a physician in order to prevent further cardiac damage and sudden death. Complications typical of coronary artery disease include angina, myocardial infarction, arrhythmia and heart failure due to loss of heart muscle. All of these complications diminish patient quality of life and without proper intervention can lead to death. Coronary artery disease is a major costly and devastating problem projected to be the preeminent health problem worldwide continuously going to year 2020 with in excess of 35 million sufferers. CAD patients that develop angina are initially treated medically with drugs and visit their physician on a regular basis provided the angina remains stable. For those individuals with resting angina, additional testing such as an angiogram and/or other tests are conducted with treatment involving either percutaneous transluminal coronary angioplasty (PTCA)/stent or coronary artery bypass grafting (CABG). Unfortunately, PTCA/stent patients often develop restenosis, requiring further testing and additional repeat procedures to correct recurrent angina. Alternatively, bypass grafts tend to occlude or otherwise develop stenoses over time resulting in recurrent angina, MI, arrhythmia, and heart failure which can lead to death. Myocardial infarctions associated with CAD afflict more than 1 million patients in the U.S. annually with many of which die suddenly therefrom worldwide with this estimate is over 3 million. As a result, CAD patients require regular physician maintenance visits to detect and possibly prevent complications and slow the debilitating effects thereof. Nonetheless, a risk of sudden and premature death from CAD remains as well as loss of heart function. Because very frequent follow up of each patient is impractical, expensive and can plague clinics and hospitals severely, there exists a need to prevent sudden death and the complications of CAD by monitoring of blood flow within coronary arteries.
Currently, the monitoring of blood flow within a native coronary artery or bypass graft requires the use of an angiogram. Intervention is dictated by a drop in blood flow which cause angina or by an MI as the native coronary artery or bypass graft occludes. An angiogram is an invasive test involving inherent risks associated with the imaging dye. Other angiogram associated risks include vascular complications such as stroke, emboli, ischemic leg, cardiac complications and renal damage. Without the ability to intervene early in the development of CAD, many unnecessary deaths result, as well as a diminished quality of life for patients owing to CAD complications resulting in huge economic losses and major expenses.
The dangers associated with an angiogram become more pressing with the increasing number of heart transplant operations performed especially if xenotransplantation is successful in the future. Approximately 50% of heart transplant recipients develop graft CAD within five years of the procedure. While heart transplant recipients do not develop angina owing to heart denervation during the transplant procedure, yearly or more frequent angiograms to diagnose the development of CAD are required with all the risks and expenses associated therewith. Further, heart transplant recipients bear an unacceptable risk of sudden death through myocardial infarction.
Periodic and/or continuous monitoring of coronary blood flow has been recognized as a means to allow early detection, management and intervention before CAD patients decompensate. Prior art attempts to continuously monitor blood flow have involved the implantation of a sensor with percutaneous leads exiting the patient to power and/or relay sensor data to an external monitor. Such prior devices have suffered from a variety of limitations that limit the usefulness thereof, these limitations having illustratively included infection and diminished quality of life associated with percutaneous leads, incompatible data collection regarding different parameters associated with cardiac function, inability to monitor single vessel throughput and the necessity for continual physician contact to monitor sensor output.
Thus, there exists a need for a wholly implantable blood flow monitoring system to provide early warning to follow blood flow within coronary arteries or bypass grafts and evaluate heart wall motion. Such a blood flow monitor system would allow for the evaluation of new myocardial revascularization processes, allow physician intervention before stenosis or occlusion of a vessel causes CAD complications such as death and allow physicians to follow heart function to see if it improves with treatment.